Related-art liquid droplet ejecting apparatuses perform a printing operation on a recording medium by moving a head unit for ejecting ink droplets while facing the recording medium in order to perform a scanning operation. JP-A-2005-161761 describes a head unit which is laminated on a reinforcing plate, and the head unit and the reinforcing plate are attached to a head holder as a set.
FIG. 9 is a diagram illustrating the head unit, the reinforcing plate, and the like included in the related-art ink-jet printing apparatus. FIGS. 10A and 10B are diagrams illustrating a configuration of the head unit and the reinforcing plat shown in FIG. 9. FIG. 10A is a top view illustrating the configuration of the head unit and the reinforcing plate and FIG. 10B is a sectional view illustrating the head unit and the reinforcing plate taken along an arrow XB-XB in FIG. 10A.
A head unit 30 includes a cavity unit 50 includes an ink flow path formed therein and a piezoelectric actuator 40 adhered on the upper surface of the cavity unit 50. As shown in FIG. 10B, the cavity unit 50 has a structure in which eight plate members are laminated and each plate member is adhered to the adjacent plate member with adhesives (not shown). A nozzle plate 38 is disposed in the lowermost portion of the cavity unit 50. The nozzle plate 38 includes a plurality of nozzle rows in which a plurality of nozzles for ejecting ink droplets are arranged. A cavity plate 31 is disposed in the uppermost portion of the cavity unit 50. The cavity plate 31 includes ink supply holes 31a to 31d and a plurality of pressure chambers for storing ink to be ejected from the nozzles.
The head unit 30 is fixed to the head holder (which is denoted by Reference Numeral 9 in FIG. 3) with the reinforcing plate 60 interposed therebetween. The reinforcing plate 60 is formed so as to have a width larger than that of the head unit 30. The reinforcing plate 60 includes an opening 60e for exposing a piezoelectric actuator 40 at the time when the reinforcing plate 60 is adhered to the head unit 30, and ink supply holes 60a to 60d for supplying ink to the ink supply holes 31a to 31d of the head unit 30. The reinforcing plate 60 is adhered to the head unit 30 by a thermoplastic sheet-shaped adhesive 2.
The sheet-shaped adhesive 2 is formed in a sheet shape corresponding to a plane shape of the cavity unit 50. The sheet-shaped adhesive includes an opening 2e for exposing the piezoelectric actuator 40, and through-holes 2a to 2d which correspond to the ink supply holes 60a to 60d of the reinforcing plate 60 and the ink supply holes 31a to 31d of the head unit 30.
When the reinforcing plate 60 is adhered to the head unit 30 by the sheet-shaped adhesive 2, high adhesive strength is necessary. For this reason, large load and sufficient heat are applied between the reinforcing plate 60 and the head unit 30. Consequently, the sheet-shaped adhesive 2 interposed between the reinforcing plate 60 and the head unit 30 is squeezed so as to become thin, and the high adhesive strength can be obtained and rigidity of the head unit 30 becomes increased.
However, in the related-art ink-jet printing apparatus, the sheet-shaped adhesive 2 between the plate members 60 and 50 surrounding ink flow paths constituted by the ink supply holes 60a to 60d and the ink supply holes 31a to 31d is always exposed to ink. Consequently, ink may enter into from an interface 2i (FIG. 10B) of the plate members 60 and 50 and the sheet-shaped adhesive 2, thereby detaching the plate members from each other. In particular, if a portion surrounding the ink flow paths in the laminated plates is distorted, a gap between the distorted portion and the adhesion layer is generated. Consequently, ink may enter into the gap, thereby detaching the plate members from each other. Moreover, in the ink-jet printing apparatus which performs a printing operation using a plurality of color ink, entering color ink may be mixed in the ink flow paths, resulting in deteriorating a print quality.